根据特殊性质来的

#include <bits/stdc++.h>
using namespace std;
const long double e = 2.7182818284590452353608747135266249;
long double n;
long double fac(long double n){
	return n ? n * fac(n - 1) : 1;
}
int main(){
	cin >> n;
	if(n == 1) cout << 0;
	else if(n == 2) cout << 1;
	else if(n == 3) cout << 2;
	else{
		cout << (unsigned long long)(round(fac(n) * (1 / e)));
	}
	return 0;
}